Limit switch with high hysteresis

ABSTRACT

A limit switch means including a magnetic transducer comprising a stator and rotor which supplies electrical energy to an associated comparator circuit. The output of the comparator circuit is connected to the gate of a silicon controlled rectifier and a voltage boosting device. The magnetic transducer is sensitive to changes in angular position of the rotor which is coupled mechanically to an associated cam, lever or similar component. When the relative position of the associated component is changed, the rotor is moved to such a position as to cause the voltage comparator circuit to supply a signal to the silicon controlled rectifier&#39;&#39;s gate sufficient to energize or turn on the silicon controlled rectifier. This allows current to flow through one or more circuits to which the silicon controlled rectifier is connected. In addition, where desired transformer coupling may be provided to drive or control other circuits whose functions may be complementary to that of the circuit which is primarily controlled. A voltage boosting means responds to the turning on of the silicon controlled rectifier in such a manner as to create a hysteresis effect by making use of an increase in the voltage at the gate of the silicon controlled rectifier so that the rotor of the associated magnetic transducer must move a substantial amount in the opposite direction to deenergize the silicon controlled rectifier and consequently change the operating condition of any circuits which it controls.

United States Patent Reeves et al.

[ 1March 13, 1973 LIMIT SWITCH WITH HIGH HYSTERESIS [75] Inventors: JohnR. Reeves, Trafford, Pa.; Bruce R. Dow, Altamonte Springs, Fla.; FrancisT. Thompson, Murrysville, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: June 7, 1971 [21] Appl. No.: 150,575

[52] U.S. Cl. ..307/116, 3l7/DlG. 2

[51] Int. Cll ..H0lh 36/00 [58] Field of Search ..307/1 16; 3l7/DIG. 2;340/266;

[56] References Cited UNITED STATES PATENTS 2,886,754 5/1959 Ehret..3l7/DIG. 2

3,207,917 9/l965 Martin.. ..3l7/DIG. 2

3,161,387 l2/l964 Jutier ..3l7/DlG. 2

Primary Examiner--Herman J. Hohauser Assistant Examiner-William J. SmithAttorney-A. T. Stratton and C. L. McHale [57] ABSTRACT A limit switchmeans including a magnetic transducer comprising a stator and rotorwhich supplies electrical energy to an associated comparator circuit.The output of the comparator circuit is connected to the gate of asilicon controlled rectifier and a voltage boosting device. The magnetictransducer is sensitive to changes in angular position of the rotorwhich is coupled mechanically to an associated cam, lever or similarcomponent. When the relative position of the associated component ischanged, the rotor is moved to such a position as to cause the voltagecomparator circuit to supply a signal to the silicon controlledrectifiers gate sufficient to energize or turn on the silicon controlledrectifier. This allows current to flow through one or more circuits towhich the silicon controlled rectifier is connected. ln addition, wheredesired transformer coupling may be provided to drive or control othercircuits whose functions may be complementary to that of the circuitwhich is primarily controlled. A voltage boosting means responds to theturning on of the silicon controlled rectifier in such a manner as tocreate a hysteresis effect by making use of an increase in the voltageat the gate of the silicon controlled rectifier so that the 'rotor ofthe associated magnetic transducer must move a substantial amount in theopposite direction to deenergize the silicon controlled rectifier andconsequently change the operating condition of any circuits which itcontrols.

23 Claims, 12 Drawing Figures PATENTEDMAR 3197s 45 SHEET 10F 5 12c FIG.|

PATENTEDHAR 1 31973 SHEET 2 OF 5 NQE PATENTEDMAR 1 31913 SHEET 0F 5 TIME(SEC) Wmin) T I 6 B T w u M T n S M I G 6 R B [A I W 6 5 m 7 5 A n t 2 6I 7 B 9 5 R FIGJI PATENTEBHARI 3|973 SHEET 5 BF 5 LIMIT SWITCH WITH HIGHHYSTERESIS BACKGROUND OF THE INVENTION This invention relates to limitswitches and it has particular relation to solid state limit switcheswhich are .adapted to cooperate with electromagnetic transducers.

In certain types of electrical apparatus such as variable reluctancemagnetic circuits of the type disclosed in U.S. Pat. Nos. 3,152,311,3,394,363, and 3,517,362, rotating members are actuated to move so as toalter or change flux paths in stationary magnetic members of atransducer. The variations in flux paths are the means whereby thechanges in position or movements of the movable rotating member aresensed.

In other types of electrical apparatus, static control devices, such assilicon controlled rectifiers, form part of electrical circuits of thetype disclosed in U.S. Pat. No. 3,493,838 where a capacitive device orsome similar element is used to control the gate of a silicon controlledrectifier.

Magnetic transducers of the type previously described present a numberof problems, one of which is lower sensitivity, that is, the ability todetect or respond to very small changes in rotational position of therotating member provided. Another problem is flux crowding, whereby thenumber of magnetic lines of flux per unit area of magnetic sectionvaries during the normal operation of the magnetic transducer. This canhappen in a number of ways, the first of which is shown in previouslymentioned U.S. Pat. No. 3,517,362 in which J. A. Mead discloses amagnetic transducer in which the number of flux lines varies through agiven cross-section as the rotary member turns. In U.S. Pat. No.3,152,311, N. N. Bojarski also discloses a magnetic transducer in whichthe cross-sectional area varies as the rotating member turns. In eithercase, the number of magnetic flux lines per unit area or flux densityvaries as the rotating member of the magnetic transducer operates. Thiscauses proportional increases and decreases in undesirable heatdissipation and eddy currents in the magnetic material from whichcertain parts of the transducer are form ed. In addition, theconstruction of known magnetic transducers of the type described is notmaximized by providing for shapes of the parts of the magnetic structurewhich are arranged or constructed to accommodate a predeterminedmagnetic flux density.

In U.S. Pat. No. 3,493,838 by L. Gyugyi et al., a capacitive storagemeans is used in conjunction with the gate of a silicon controlledrectifier with the capacitive element operating to trigger the siliconcontrolled rectifier rather than to maintain it in its energized state.

SUMMARY OF THE INVENTION ln accordance with the invention, a generallyrectangular shaped magnetic stator, which may be laminated, has fourgenerally equally spaced inwardly facing poles. The first of these polesis surrounded by a bobbin on which is disposed a winding or coil havinga plurality of turns of a coiled wire or conductor, the ends of whichare adapted to be connected to a source of alternating current. The coilor winding is disposed in inductive relation with the adjacent polepiece, to produce magnetic flux when energized. Adjacent to this primarypole and on either side of it is a pair of oppositely disposed poles.These latter poles have similar bobbins surrounding them with eachbobbin having disposed thereon a coil or winding having a plurality ofturns of electrically conducting wire. Disposed along the innerperiphery of the stationary magnetic structure is a fourth stationarypole which has no winding disposed thereon. All four magnetic poles haveconcave surfaces such that a generally circular movable magnetic memberor rotor may rotate in close proximity to all four stationary poles. Thegenerally circular rotor has two complementary or opposite convexsurfaces or poles which conform closely to the shape of the previouslymentioned stationary poles thus minimizing the air gaps between therotor and the associated poles. The first convex curved or arcuatesurface on the rotor is normally aligned adjacent to the previouslymentioned primary stationary pole and is slightly larger in acircumferential sense than said pole so that the curved surface of therotor may rotate within a predetermined range or sector and stillpresent substantially the same surface area to the primary or excitationpole. Oppositely disposed on the centrally pivotable rotor is an evenlarger pole portion having a radius which allows it to rotate among thetwo other oppositely disposed poles having windings thereon and the polewhich has no electrical winding disposed thereon. The periphery of thelatter pole portion of the rotor is large enough that it presents acontinuous surface to the stationary pole without any winding and partof said pole is disposed adjacent to the other two adjacent poles duringa normal operating condition. Consequently, flux produced in the primarystationary pole due to the magnetomotive force of the associated windingwhen energized passes through the rotor to the oppositely disposedstationary pole whereupon the magnetic flux lines split and dividesubstantially equally around the remaining sides of the generallyrectangularly shaped stationary magnetic structure or stator. Inaddition, a small amount of magnetic flux is shunted through the firstand second adjacent stationary poles and through the remainder ofthestationary magnetic structure, with all branches of magnetic fluxreturning to the primary stationary pole. The small amounts of leakageflux which flow through the adjacent oppositely disposed stationarypoles are inductively coupled to a sensitive output electrical circuitin each case. It should be noted that in the magnetic circuits of therotor or stator, the relative magnetic flux per unit area does notchange substantially; consequently, the entire transducer may bedesigned to accommodate a specific or predetermined magnetic flux. Itshould also be noted that the pole portion on the rotor which overlapsthe stationary pole which does not have a winding disposed thereon andthe pair of adjacent stationary poles only slightly shades or overlapsthe latter poles so that if the rotor is moved or rotated only slightly,the total amount of magnetic flux flowing through each of the respectiveoppositely disposed pair of stationary poles changes substantially interms of percentage, although the magnetic flux per unit area or fluxdensity in each of said poles does not change appreciably. Consequently,a rotation of the rotor of only a few degrees may double or even triplethe output current in one of the inductively coupled output windings,whereas it would correspondingly reduce by half or reduce by a factor of3 the current in the other oppositely disposed output winding. Thisindicates the sensitivity of the magnetic transducer. Since the rotormay be coupled to a lever or cam or some similar device which moves orrotates due to various mechanical functions performed in the vicinity ofthe cam or lever a slight change in angular position will cause asubstantial change in the relative output currents associated with thetwo adjacent oppositely disposed poles.

The two output currents of the magnetic transducer in turn are appliedto a voltage comparator where they are converted to voltage signals,each of which is compared against the other to produce an output voltagesignal which is proportional to the difference in voltage which, inturn, is substantially proportional to the angular deviation of therotor from a central reference position. When the rotor is in itscentral reference position, the amount of magnetic flux flowing througheach of the oppositely disposed output poles is substantially equal;therefore, the induced output currents are substantially equal inmagnitude. When applied to the voltage comparator and converted to avoltage signal, the two output currents therefore produce an outputpotential or voltage which is substantially zero. When the rotor movesaway from the central reference position a predetermined number ofdegrees, the output voltage of the voltage comparator is sufficient toapply a triggering voltage to the gate of an associated siliconcontrolled rectifier or similar device and turn it on.

Another aspect of the applicants invention concerns a silicon controlledrectifier with an associated protective capacitor and resistor circuitwhich is connected to two terminals of a diode bridge network as themiddle leg of a diode bridge network. The other two terminals of thediode bridge network (those not connected to the terminals of thesilicon controlled rectifier) are connected in series to a source ofalternating current and a load which typically constitutes a relay coil.In addition, the relay coil may be shunted by a transformer primary coilor winding. The connections of the bridge network, source of alternatingcurrent, and the relay coil or load are arranged so that when thesilicon controlled rectifier is energized or conducts, current flowsthrough the relay coil or load thus actuating the relay to perform apredetermined function. Conversely, when the silicon controlledrectifier or similar device is off or deenergized, substantially nocurrent may flow through the previously mentioned relay coil. The gateterminal of the silicon controlled rectifier is connected to the outputterminal of the aforementioned voltage comparator and to a voltageboosting circuit which may be either of two types, as will be describedlater.

Normally, when sufficient positive voltage exists at the output terminalof the voltage comparator network, such as would be the case if therotor were moved from the central reference position to produce arelatively greater output current in one of the inductively coupledoutput circuits than in the other inductively coupled output circuit,the silicon controlled rectifier will be turned on and thus conductcurrent through the associated relay coil. Under normal circumstances,the current being conducted through the relay coil will tend to bebidirectional alternating current having the characteristic shape of asine wave. Normally, the presence of the previously mentioned triggeringvoltage at the gate of the silicon controlled rectifier will only turnthe rectifier on and as is known, will not substantially affect theoperation of the silicon controlled rectifier again until the siliconcontrolled rectifier has been turned off or actuated to a substantiallynon-conductive state by other means, such as a reduction in the voltageacross the anode and cathode of the silicon controlled rectifier to avalue generally below the value of the voltage on the gate of thesilicon controlled rectifier. However, in one embodiment of theinvention, a capacitor is connected between the gate and the cathode ofthe silicon controlled rectifier so that once sufficient voltage hasbeen generated in the voltage comparator network to turn the siliconcontrolled rectifier on, certain operation take place which cause thesilicon controlled rectifier to remain on even though that the outputvoltage of the voltage comparator should decrease to a value which wouldotherwise turn the silicon controlled rectifier off. This arrangementcreates a positive hysteresis effect which allows the disclosed limitswitch to be insensitive to slight mechanical vibrations, slightdeviations in the source current, slight variations in componenttolerances, and extraneous noise voltage pickup.

The operation whereby the silicon controlled rectifier is caused toremain on is as follows: once the silicon controlled rectifier is turnedon, anode current flows through a resistance which will be called theanode-tocathode resistance of the anode-to-cathode circuit. Since thecurrent flowing is substantial, it will create a substantial increase involtage between the gate and cathode due to the voltage drop across thatpart of the anode-to-cathode resistance which is also connected betweenthe gate and cathode. Since the previously mentioned capacitor isconnected between the gate and cathode, the voltage across it mustincrease to the same value because the capacitor acts as an energystorage means for current which flows out of the gate of the siliconcontrolled rectifier due to the increase in gate-to-cathode voltage.Consequently, when the tendency occurs for the silicon controlledrectifier to turn itself off because the current flowing through thepreviously mentioned anode-to-cathode circuit or resistance decreases,the associated capacitor will return charge to the gate for a shortperiod of time to maintain the silicon controlled rectifier in its onstate until the next half cycle of the previously mentioned full waverectified current appears. Consequently, this capacitive voltageboosting network acts as a holding or sustaining circuit and as ahysteresis creating circuit.

In another embodiment of the invention which may be used at lowertemperatures, a solid state transistor is used in conjunction with afeedback means to accomplish the same function as the previouslydiscussed capacitive voltage boosting network.

Finally, as previously mentioned, the relay coil or load of the solidstate limit switch may have a transformer primary winding connectedacross it. The secondary of the same transformer may be connected to asecond full wave rectifier circuit with a silicon rectifier and a secondexternal load circuit containing a second relay coil. This switchingcircuit is electrically coupled to the first switching circuit throughthe previously mentioned transformer in a complementary manner so thatwhen the first switching circuit or first silicon controlled rectifieris conducting, the second switching circuit is substantiallynon-conducting and, alternatively, when the first switching circuit issubstantially non-conducting, the second switching circuit isconducting. This combination forms a relay system where there is a mainset of relay terminals and an auxiliary set of relay terminals which areactuable to opposite conducting states.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of the magnetictransducer used in the solid state limit switch;

FIG. 2 is a schematic diagram of one embodiment of the solid state limitswitch;

FIG. 3 is a superimposed plot or graph of transducer output voltageversus transducer rotor position;

FIG. 4 is a schematic diagram of part of the comparator circuit andcapacitor voltage boosting network as used in the primary embodiment ofthe invention;

FIG. 5 is a plot of comparator output voltage versus transducer rotorposition;

FIG. 6 is a schematic diagram similar to the schematic diagram shown inFIG. 4 with the addition of a partial equivalent circuit for a siliconcontrolled rectifier;

FIG. 7 is a schematic diagram similar to that shown in FIG. 6 with theaddition of another possible equivalent circuit for a silicon controlledrectifier;

FIG. 8 is a plot of silicon controlled rectifier gate voltage versustransducer rotor position;

FIG. 9 is a schematic diagram similar to the schematic diagram shown inFIG. 7, with an element added for the transient response of the siliconcontrolled rectifier;

FIG. 10 is a plot of the transient response of the silicon controlledrectifier as a function of time;

FIG. 11 is an equivalent circuit for a silicon controlled rectifier; and

FIG. 12 is a schematic diagram of another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,and FIG. 1 in particular, the switching member 10 shown therein maycomprise a generally rectangularly shaped magnetically conducting statoror stationary support member 12 which may be formed from laminated,metallic soft magnetic material such as indicated at 12A and 12B, and apair of adjacent preferably non-magnetically conducting rotor supportingmeans or structures 13A and 138 which may be attached or secured tostator 12 by suitable means such as a plurality of bolts or fasteningstructures one of which is shown at 13C. Switch 10 also comprises arotating member or rotor 14 with oppositely disposed magnetic polesections 14A and 14B. Rotor 14 may be made of a soft magnetic materialwhich may be laminated, such as an alloy of iron or steel, to conduct orprovide a low reluctance path for magnetic flux. Poles or pole sections14A and 143 have outer peripheries or perimeter sections 15A and 158which are generally convex, curvilinear surfaces. Rotor 14 may besupported on adjacent supporting means or legs 13A and 133 by means of ashaft 18 on which the rotor 14 is mounted and which is free to rotate inthe opening 16 provided in supporting means 13A and a similar opening(not shown) in supporting means 133. Shaft 18 is capable of rotating indirection 19CW or 19ACW to cause rotor 14 to change position angularlywithin the inner periphery of stator structure 12.

Stator or stationary magnetic structure 12 comprises four internallydirected stationary magnetic poles 20, 22, 24 and 26 where poles 20, 22,24 and 26 may be made of the same material as stator section 12. Each ofthe poles 20, 22, 24 and 26 has a concave inner periphery or surface asindicated at 20C, 22C, 24C and 26C, respectively, which generallyclosely corresponds in radius of curvature to the convex pole sectionsor surfaces 15A and 153 on rotor 14, so that the rotor 14 may movefreely among the poles 20, 22, 24, 26 in such a manner that convexsurfaces 15A and 15B on rotor 15 may rotate in close proximity toconcave surfaces 20C, 22C, 24C and 26C to establish substantiallyuniform air gaps between mating parts of poles 20, 22, 24 and 26 androtor poles 14A and 14B. This is not to say that surfaces 15A and 15Bneed necessarily overlap or become adjacent to all of stator polesurfaces 20C, 22C, 24C and 26C concurrently.

Stator pole 20 will hereinafter be referred to as third pole or mainpole of switching section or transducer 10 and serves to conductmagnetic flux from stator section 12 through main or input pole 20 intorotor section 14 with the magnetic flux passing generally through thegap between surfaces 20C and 15A of the respective poles 20 and 14. Alsomounted on stator section 12 and disposed approximately degrees away inangular displacement in each direction from main or input pole 20, areoppositely disposed output poles 22 and 24 which will hereinafter bereferred to as first and second stator output poles, respectively.Output poles 22 and 24 are adapted to conduct magnetic flux from rotorpole 148 in such a manner that the flux may flow from convex surface 158through a gap across convex surface 22C or convex surface 24C or both ofsaid surfaces and continue through poles 22 or 24 and around magneticstator 12 back to the vicinity of input pole 20. It is generallycontemplated that rotor 14 may be positioned so that a slight but notnecessarily equal overlap or shading of pole 158 by each of poles 24 and22 is likely. In such a case, magnetic flux may flow as previouslydescribed through both poles 24 and 22 from rotor 14. However, shouldthe position of rotor section 14 be changed substantially angularly ineither direction 19CW or direction 19ACW by a predetermined angle ornumber of degrees, it may be possible for only one of the poles 22 or 24to have a surface (22C or 24C) which overlaps surface 158 of rotor pole14B so that magnetic flux is conducted through only one ofthe poles 24or 22.

Magnetic pole structure or main pole 20 has an input coil or winding 28mounted there on and disposed in inductive relation with it so that whenelectric current flows through a plurality of electrically conductingturns which form part of the coil 28, magnetic flux lines are producedor generated in pole 20 which travel or flow through portions of therotor 14 and stator 12. In addition, poles 22 and 24 have disposed ininductive relation therewith coils or windings 30 and 32, respectively.so that magnetic flux which passes into either or both of poles 22 and24 may induce first and second electrical currents into either or bothof coils 30 and 32, respectively, each of which includes a plurality ofelectrically conducting turns.

Finally, there is magnetic pole 26 also disposed on the inner peripheryof stator structure 12. Magnetic pole structure or pole 26 is disposedgenerally opposite pole 20 and spaced approximately 90 along the innersurface of the magnetic structure 12 from each of output poles 22 and24. Pole 26 has no inductive coil surrounding it and merely acts as aconductor of some of the magnetic flux which is generated or produced inmagnetic pole 20 and carried through rotor 14. Thus, pole 26 acts tocomplete the return path for a substantial portion of the previouslymentioned magnetic flux through stator section 12.

In general, switch structure or transducer has a reference position 21in which rotor 14 is substantially aligned with surface B of rotor 14overlapping concave surfaces 22C and 24C by relatively small butsubstantially equal amounts. When rotor 14 is disposed in the referenceposition 21, magnetic flux generated or produced in pole as a result ofcurrent flowing in coil 28, is conducted through rotor 14 to polesections 22, 24 and 26 with most of the magnetic flux being conductedinto pole section 26 and around the outer periphery of stator 12 back tothe pole 20.

Referring now to FIG. 2, the possible paths that magnetic flux may takethrough stator section 12 are indicated. It should be noted that current121i flowing in lines 44 to coil 28 generates or produces magnetic fluxas indicated by 123, 125, 127 and 129 within magnetic pole or polesection 20. Some magnetic flux then flows into and substantially throughrotor 14, as indicated by dotted lines 123 and 125. The flux indicatedby the dotted lines 123 and 125 flows completely through rotor 14 topole 26 whereupon flux indicated by the line 123, flows through theupper part 17A of stator 12 and flux indicated by the line 125, flowsthrough bottom part 17B of stator 12, whereupon said magnetic fluxesjoin again in the vicinity of pole 20. In addition, magnetic flux linesindicated at 127 may be diverted away through magnetic pole structure22, the stator section 12 and back into main pole or input pole 20.Similarly, magnetic flux as indicated at line 129 may flow throughmagnetic pole 24 and through the remainder of stator 12 to rejoin theother previously mentioned flux lines in magnetic pole 20.

As can be seen by close examination of the transducer section 10 in FIG.2, slight rotation of the rotor 14 in direction 19CW or direction 19ACWwill cause more surface area of the rotor 14 at pole 15B to overlapeither stationary pole 22 or 24, thus allowing more magnetic flux toflow through one of said poles, such as pole 22, and less flux to flowthrough the oppositely disposed pole, such as pole 24. Since the moremagnetic flux that flows through either pole 22 or pole 24, the moreelectrical current is generated in the respective coils 30 or 32, therelative magnitudes of corresponding output current l3ll, 133I willdiffer depending on the relative position of rotor 14 with respect toreference line or normal position 21. Consequently, any operation whichcauses shaft 18 to rotate, such as the movement of part of an associatedmachine tool which engages a toggle, cam or gear or some similarmechanical means attached to shaft 18 will change the position of rotor14 and thus change the relative value of output currents 131i and 133]to reflect the change in position of the rotor 14.

It will be seen in FIG. 2 that output currents [3H and 1331 from thetransducer 10 are applied to bridge networks 52 and 54, respectively.Bridge networks 52 and 54 along with the innerconnected combination ofresistors 58 and 60 comprise a voltage comparator network 50. It isnoted that the phase of the voltage and current generated in bridgecircuit 52 is out of phase with that of the current and voltagegenerated in or applied to bridge network 54. Consequently, full wavebridge rectifier network 52 supplies voltage or potential V52 toterminal 47A which is positive with respect to potential V54 at terminal49A of bridge network 54. Both voltages V52 and V54 representunidirectional pulsating signals which generally do not change polarity.The resistances of resistive elements or resistors 58 and 60 are ofgenerally equal value, such that the voltage V134 at node or junctionpoint 62 reflects the relative absolute difference between voltage V52and V54. As an example, when rotor 14 is at its neutral or normalreference position 21 the currents 131i and 1331 are substantially equaland the cor responding voltages V52 and V54 are substantially equal;consequently, the voltage V134 at junction point 62 with respect tocommon terminal 51 of the two bridge networks 52 and 54 is approximatelyzero. Should current 131] increase and current 133] decrease, as wouldbe the case if rotor 14 were moved in the direction 19ACW, then voltageV52 would increase and voltage V54 would decrease resulting in a voltageV134 at junction point 62 which is slightly positive with respect to thecommon terminal 51 or of the same polarity as voltage V52.

Connected to junction point 62 is a voltage boosting means 64A, morespecifically capacitive element 65, and the gate 76 of a siliconcontrolled rectifier or thyristor or gated static switching means 68.Voltage boosting means 64A which comprises capacitor 65 is connected tojunction point 62 at junction point or positive terminal 63 of capacitor65. Generally, junction point 62, junction 63 and gate 76 have the samepotential value during static operation and differ only slightly involtage value during dynamic operation. The combination of voltage V134and that portion of the current 1341 flowing into gate 76 may besuitable to trigger or turn on silicon controlled rectifier 68 dependingupon the relative magnitude and polarity of alternating voltage source42 as supplied to the silicon controlled rectifier anode 72 and cathode74 through the full wave bridge rectifier network 70. In any event, theremaining portion of current 134] which does not flow into gate 76 flowsinto capacitor 65 to charge capacitor 65 so that the voltage at terminal63 is substantially the same potential as the voltage at terminal 62,namely voltage V134.

Switching circuit 66 comprises gated static switching means 68 and thepreviously mentioned full wave bridge rectifier network 70. Siliconcontrolled rectifier 68 comprises an anode 72, a cathode 74, and acontrol element or gate 76. The anode 72 and cathode 74, respectively,are connected to a source of unidirectional current or pulsating,rectified alternating voltage, as is produced by full wave bridgerectifier network 70 from a source of alternating current 42. When thegate to cathode voltage V135 exceeds the switch on voltage of SCR 68,the SCR conducts. This causes current to flow through line 80 during apositive half-cycle of alternating current voltage from source 42 tobridge diode 7313 into bridge terminal 70C and consequently, to anode 72of silicon controlled rectifier 68. The cur rent then flows through theanode-cathode circuit of silicon controlled rectifier 68 to cathodeterminal 74 and to bridge terminal 70D through bridge rectifier or diode73A and then to lead or wire 81. Load current 800i flowing through leador line 81 is returned to the source of alternating current 42 throughan alternating current type relay coil 82 having associated therewith amovable arm or slug 88.

The flow of a significant portion of current 8001 through through relay82 energizes relay coil 82 to close contact means 90 which may compriseone or more contacts 90A, 90B, 90C as illustrated, so as to connectcircuits 92 and 94 to thereby perform a predetermined control function,such as changing the direction of movement of a cutting edge, forexample, on a controlled machine tool 27. During the negative half-cycleof the alternating current source 42, current flows in a reversedirection through alternating current coil 82 causing relay contacts 90to remain closed. The current at this time flows through line 81, bridgerectifier diode 73C, through silicon controlled rectifier 68 in a mannersimilar to that just described and through bridgeiircuit' aisae 75D andtoline 86 where the current is returned to the alternating currentsource 42. As can be seen, alternating (pulsating) current flows throughcoil 82 energizing it during both positive or negative half-cycles ofsource 42, However, bridge network 70 permits current to flow in onlyonedire ction through silicon controlled rectifier 68, Thus, siliconcontrolled rectifier 68 will remain in a conducting state provided thatno significant negative voltage signal V134 is applied to gate 76.Silicon controlled rectifier or static switching means 68 may beprotected by a noise suppression network 71 comprising a resistor 71Aand capacitor 718.

The alternating (pulsating) voltage is also provided to the secondary 87of transformer 85 through the primary winding 86 of transformer 85.Current is supplied alternately through diodes 101A and 101B tocapacitor or second voltage boosting means 96 and gate 103 of thyristoror second silicon controlled rectifier or slaved switching means 100.Biasing resistors 106 and 108 are connected in series between the anodeand cathode of the controlled rectifier 100. Slave circuit 105 whichincludes transformer secondary 87, capacitor 96, silicon controlledrectifier 100, bridging means 104, and second or complementary relaycoil 112 acts similarly to the previously described switching circuit64A, except that the phasing of the voltages across the primary and thesecondary windings 86 and 87, respectively of transformer 85 arearranged so that slave circuit 105 may operate in a complementary mannerto the circuit which includes switching means 66. That is, when siliconcontrolled rectifier 68 is conducting, causing coil 82 to be energizedby load current 8001, thus closing contacts 90, slave or complementarycircuit 105 is deenergized, causingcoil 112 to also be deenergized so asto ass'rniamaany closed coarser means "116 which may include three phasecontacts 116A, 1168 and 116C. The contact means 116 may be disposed toconnect circuits 118 and 120 where circuits 118 and 120 may also bearranged to control a function of an associated machine tool. Theoperation of circuit 105 is similar to that of the previously describedswitching circuit which includes circuits 50, 64A and 66. In otherwords, the operation of the silicon controlled rectifier or switch meansin combination with the boosting means and voltage comparator circuit,will be the same as that described with respect to the primary switchingmeans 66 of the switch 40 with the understanding that circuit operatesessentially in the same manner.

it is desirable that silicon controlled rectifier 68 and the switchingmeans 66 of which it is a component have a hysteresis or off delayoperating characteristic. That is, silicon controlled rectifier 68should be so controlled that once gate 76 has been energized to actuatesilicon controlled rectifier 68 to pass current, it should remainenergized even under the influence of slight variations in voltage V134.The value of voltage necessary to trigger or turn on silicon controlledrectifier 68 should be substantially or significantly greater than theamount of voltage necessary to deenergize or turn off silicon controlledrectifier 68. As can be seen, slight mechanical rotational variations inshaft 18 or electri' cal variations in circuits 52, 54 or 64A forexample, as well as variations in transducer 10 may cause siliconcontrolled rectifier 68 to inadvertently turn off or cease to beenergized once it has been turned on. Consequently, there is a need fora hysteresis generating circuit which insures positive turn on ofsilicon controlled rectifier 68 and which provides a dead band of gatevoltage in the operation of controlled rectifier 68 to insure thatswitching circuit 66 will remain on after it has been turned on.

To accomplish this function, it must be realized as will be shown later,that substantial current flowing through the anode-to-cathode circuit(72to-74) of silicon controlled rectifier 68 causes the gate voltageVl35 of silicon controlled rectifier 68 to increase by a small butsignificant amount once silicon controlled rectifier 68 has been turnedon by the action of V134 and current 1341. This increase in voltagerepresented by voltage V135 is due to the flow of current through aresistance (not shown in FIG. 2) which may be referred to as the gatecomponent of the anode-to-cathode circuit resistance R(A-K). Currentflowing through this resistance, R(A-K), causes an increase in voltageacross it which is reflected at gate 76 resulting in the voltagerepresented by V135. This causes a current 1361 to flow toward junctionpoint 63 and into voltage boosting means 64 A, as represented in thiscase by capacitor 65. Consequently, as the pulsating current flowingthrough silicon controlled rectifier 68 which is supplied fromalternating current source 42 and rectified by rectifying means or fullwave bridge rectifier 70 nears zero, the tendency for the siliconcontrolled rectifier 68 to turn off is overcome by an increasedgate-to-cathode voltage V135, produced by the prior integration ofcurrent 1361 by capacitor 65, and the subsequent feedback current 137itherefrom. As the current provided by alternating current source 42approaches current zero, the voltage V135 begins to decrease inproportion to the anode to cathode current,

since voltage V135 is essentially equal to current times the gatecomponent of the anode-to-cathode resistance R(A-K). However, there issufficient voltage retained across capacitor 65 to maintain terminal 63at a higher voltage than gate 76, thus tending to keep siliconcontrolled rectifier 68 turned on. As voltage V135 begins to decrease,current 137I flows into gate 76 from capacitor 65 acting as a positivesource of energy to gate 76 which, in turn, actuates silicon controlledrectifier 68 to remain energized until the next current pulse fromcurrent or energy source 42 is applied to the bridge rectifier network70, significantly increasing the current through silicon controlledrectifier 68 to a value which generates a value of voltage which is inexcess of the gate voltage V135. This allows silicon controlledrectifier 68 to remain on. This sequence of operations is repeated eachhalf cycle of alternating current from the source 42 keeping siliconcontrolled rectifier 68 continuously conducting. It will therefore beunderstood that the flow of current through the gate component of theanode-to cathode resistance R(AK) is the means whereby the hysteresis inthe operation of the overall circuit previously described is effected.The fact that capacitor 65 is connected to gate 76, allows the energyfrom that voltage drop, represented by V135, to be absorbed during aperiod of time when current conduction in silicon controlled rectifier68 is insured by a high value of pulsating current from the source 42.This energy absorption is accomplished by the transfer of energy orcharge by way of current 136I to capacitor 65. Consequently, oncesilicon controlled rectifier 68 has been turned on by the presence ofcomparator voltage V134, the aforementioned voltage boosting circuit maybe used to sustain continued current conduction through siliconcontrolled rectifier 68 even though V134 may vary slightly in a negativedirection. The net effect is to force the voltage at terminal 76 to beequal to the value of V135 so that the voltage at junction point 62 israised by an amount equal to the difference between voltage V135 andvoltage V134. Therefore rotor 14 must be rotated a significant number ofdegrees or radians in the clockwise direction 19CW to provide sufficientnegative voltage V54 at point or junction 49A to cause voltage V134 atjunction point 62 to change to a value sufficiently low to deenergizesilicon controlled rectifier 68. Since it is contemplated in the firstembodiment of the invention that rotor 14 and the correspondinggenerally rigidly attached shaft 18 are actuated to rotate significantlybecause of motion in an associated component of a machine tool or somesimilar mechanical device effecting a cam, gear or lever followerattached or secured to shaft 18, silicon controlled rectifier or switch68 may be turned on by relatively large excursions or changes of voltageV134 while relatively small excursions or changes of voltage V134 due tovibrations in the associated machine tool or the like may not causesilicon controlled rectifier 68 to be deenergized or turned off. Suchsmall changes of voltage V134, correspondingly, will not cause coil 82to be deenergized. Therefore, circuit contacts 90, once closed, willremain closed to maintain electrical continuity between circuits 92 and94 unless rotor 14 is rotated significantly in a clockwise direction19CW.

Referring now to FIG. 3, a graph of output voltage for the coils 30 and32 of stator 12 versus angular rotation of the rotor 14 is shown. Inthis plot, angular rotation in radians is indicated along abscissa 140,while output voltage and alternating current voltage peak-topeak isindicated along ordinate 142. The output voltage of coil 30 isrepresented by curve 146 and the output voltage of coil 32 isrepresented by curve 144. It will be noted that the output voltage ofcoil 30 decreases from a saturation value V as the rotor 14 is rotatedin a counterclockwise direction to a value of zero output voltage, butthe output voltage of coil 32 decreases from a saturation voltage V tozero voltage as rotor 14 is rotated in a clockwise direction. As shownin FIG. 3, (01 represents the approximate angular displacement fromreference position zero or reference line 21, as shown in FIG. 1, thatrotor 14 must be rotated in the counterclockwise direction for thevoltage or current flowing from coil 32 to increase to the saturationvoltage. As shown in FIG. 3, (02 represents generally the same angulardisplacement as was described with respect to ml for the output voltageand current of coil 30 to increase to saturation. It will be noted thatat the zero point along the abscissa or generally half-way between (02and ml, curve 144 and curve 146 cross or intersect which means that theoutput voltages of coil 32 and coil 31 are substantially equal at thezero reference point or point 21, as represented on rotor 14 shown inFIG. 1. This point or crossover is indicated at 148. It is noted thatpoint or crossover 148 is not at zero output voltage, but at somepredetermined value of voltage V148. However, the difference in voltagebetween coil 32 and coil 31 as a function of angular rotation of rotor14, is substantially zero at this point. This is demonstrated moreclearly in FIG. 5 which will be discussed hereinafter.

FIG. 4 shows a schematic diagram of part of of the circuitry shown inFIG. 1. That is, the resistive part of the comparator circuit network 50and the voltage boosting means 64A or capacitor 65. As is shown in FIG.1, junction point 62 is the terminal where capacitor 65 is connected tothe series circuit combination of resistors 58 and 60. Also, voltagesV52 and V54 are indicated at points 47A and 49A, respectively. It shouldbe noted that curve or waveform 53 represents the output voltage ofbridge rectifier means 52, more specifically a positive pulsatingcurrent voltage having a maximum amplitude V131A. Pulse train 55indicates a series of negative rectified pulses having an amplitudeV133A, while curve or waveform 67 represents a filtered series ofpositive output pulses having an amplitude V134. This latter situationresults where the magnitude of output voltage V52 is greater than thatof voltage V54, the difference voltage being a voltage having themagnitude V134 and being positive in polarity. The smoothing orfiltering of the voltage V134 is done by the multi-purpose capacitor 65.

FIG. 5 shows graphically the output voltage of the voltage comparator 50as a function of rotation of rotor 14. The ordinate 162 indicates theoutput voltage in direct current'volts and the abscissa indicates therotation of the rotor in angular radians. The quantities m1 and (.02 arethe same quantities indicated as ml and (02, respectively, in FIG. 4.Generally, curve 146A corresponds to curve 146 of FIG. 3 and curve 144Acorresponds to curve 144 of FIG. 3. It will be noted that point MBA orthe zero point in FIG. corresponds to point 148 in FIG. 3. This is thepoint where there is substantially no net output voltage because thereis no difference between the voltages generated in coil 30 and coil 32.Consequently, this indicates a value of zero volts for voltage V134 atpoint 62, as shown in FIG. 4, with the waveform curve 67 therefore beinga generally straight horizontal line, representing zero voltage for thisoperating condition.

Referring now to FIG. 6, resistors 58 and 60 which were shown in FIG. 5are shown again in FIG. 6 as is capacitor 65. Voltage V134 is indicatedat junction point 62 and capacitor terminal 73 which for most purposesare substantially the same points electrically. Also connected tojunction point 62 and having substantially the same voltage or potentialV134 is gate terminal 76. Shown connected between gate terminal 76 andcathode terminal 74, is an intrinsic equivalent circuit for a siliconcontrolled rectifier or gated switching means 68. There is an equivalentresistance R and an equivalent reverse voltage V,,,,,,. In actualoperation, the voltage V134 must overcome or be greater than V,,,,,, orthe minimum firing voltage of the silicon controlled rectifier 68 inorder for the silicon controlled rectifier 68 to conduct, and thecurrent into the gate terminal 76 of silicon controlled rectifier 68 islimited by intrinsic resistance R Referring to FIG. 7, R59 is shown asrepresenting a Thevenin equivalent circuit for resistors 58 and 60.Junction point 62 is again shown adjacent to gate 76 Again, anequivalent circuit is shown which extends between gate terminal 76 andcathode terminal 74, and as was the case in FIG. 6, R is shown connectedto gate 76. However, a current source 13618 is shown connected in serieswith R Current source 136IS, upon energization or turning on of siliconcontrolled rectifier 68, causes a voltage V135 to be present at gateterminal 76 and a current 136I to flow into capacitor 65. As currentdecreases through the main anode-tocathode circuit (72-to-79) of siliconcontrolled rectifier 68, the value of current 136I as generated insource 136 IS decreases and the voltage drop V135 decreases inproportion to the current which flows through the anode-to-cathode(7240-79) circuit of silicon controlled rectifier 68. Consequently,capacitor 65 discharges to return some of the energy in the form ofcurrent 137I into gate 76 that was originally supplied to it by current13618, thus maintaining gate 76 of silicon controlled rectifier 68 at apotential or voltage which is sufficient to actuate the siliconcontrolled rectifier 68 to continue to conduct or maintain SCR68 in aconducting state.

FIG. 8 graphically represents what was previously described with respectto FIGJS. 6 and 7. FIG. 8 is similar to FIG. 5 in that ordinate 170represents the silicon controlled rectifier gate voltage V135 and theabscissa 168 represents the angular position of the rotor 14 withrespect to reference point 21. As can be seen, curves 146A and 144A aresubstantially the same as those shown in FIG. 5. To consider the actionof the silicon controlled rectifier gate voltage V135 as the position ofthe rotor 14 of the transducer is varied from a counterclockwisedeviation or position with respect to the reference point 21 to aclockwise deviation from the reference point 21, the following operationoccurs assuming that the rotor has been initially adjusted to an extremecounterclockwise position as represented by point 171 on curve 146.Since curve 146A and curve 144A in combination indicate voltage V134 asa func tion of the position of the rotor 14, the voltage correspondingto point 171 represents a negativesaturation voltage or negative voltageat the gate 76 of the silicon controlled rectifier 68. As the rotor 14is moved in a counterclockwise direction 19ACW as indicated by arrow172, silicon controlled rectifier 68 remains off, until after the outputvoltage V134 passes zero reference point as indicated by 133 on curve144A. However, when rotor 14 has been rotated in a counter clockwisedirection 19ACW sufficiently for the voltage comparator circuit 50 toproduce the value V,,,,,, at junction 62, as indicated in FIG. 6, thesilicon controlled rectifier 68 will conduct and immediately, asindicated at arrow 174 in FIG. 8, the voltage V134 at the gate 76 of thesilicon controlled rectifier 68 will increase by a predetermined valueso that further changes in the voltage will be along the curve 135A asshown in FIG. 8. This jump in voltage V137 represents the amount ofadditional voltage which must be overcome by rotating the rotor 14 inthe opposite or clockwise direction 19CW and contributes to thehysteresis of the switching circuit 40. As the rotation of the rotor 14is continued in a clockwise direction as indicated at 176, eventually anextreme clockwise position 177 is reached whereafter the rotor 14 isthen moved in a clockwise direction 19CW as indicated at 178 on voltagecurve 135A. Curve 135A represents the voltage V135. It will be notedthat the voltage at the gate 76 will be the voltage V135 as representedby curve 135A even after the rotation of rotor 14 has passed the minimumfiring voltage as indicated by V on abscissa 168. Consequently, it isnot until the rotor 14 has reached the zero reference point 133 or thepoint represented by line or indicator 21 in FIG. 1 that the siliconcontrolled rectifier 68 will cease to conduct or turn off as indicatedat 180 in FIG. 8. At this point, continued rotation of the rotor 14 inthe clockwise direction 19CW as indicated at 182 will retain the siliconcontrolled rectifier 68 in the off status. The excursion of the rotor 14is completed when it returns to the starting point 171.

It will be noted that shaded region 185 represents the hysteresisoperating region of the silicon controlled rectifier gate circuit 66. Inother words, this means that once the silicon controlled rectifier 68has been toward on by applying a predetermined minimum voltage valueV,,,,,, to the gate 76, a substantial clockwise rotation of the rotor 14is required as represented by angular displacement 500 shown in FIG. 8,to cause silicon controlled rectifier 68 to turn off.

Referring now to FIG. 9, a circuit similar to that shown in FIG. 7 isshown with the addition of an element 136IT which represents a transientcurrent generator. Transient current generator 136IT contributes to thetotal amount of current 136I which flows into capacitor 65 when siliconcontrolled rectifier 68 is energized and turned on.

Referring to FIG. 10, a voltage-versus-time plot for the siliconcontrolled rectifier gate 68 is shown. The voltage with respect to timefollows curve V134 until time t(V,,, is reached, in which case, thesilicon controlled rectifier voltage changes as indicated by a steeprising voltage pulse 189 to a maximum value VT. Then the value ofvoltage decreases as shown by that part of the curve 190 until plot ofthe voltage V135 with respect to time is reached, which corresponds tothe curve 135 as shown in FIG. 8. The transient voltage VT which resultsat the gate terminal 76 of silicon controlled rectifier 68, is afunction of transient current 136IT, and its large positive spike helpsin creating a positive turn on action for silicon controlled rectifier68. The transient voltage is dependent upon current 136IT flowingthrough capacitor C(G-A) as shown in FIG. 11.

Referring now to FIG. 11, an equivalent circuit for silicon controlledrectifier 68 is shown including gate G, 76, anode A, 72 and cathode K,74. This equivalent circuit comprises an anode component ofresistor-tocathode resistance R,, and a gate component R(A-K). It alsoincludes a gate-to-cathode resistive component R(GK), a gate-to-anoderesistive component R(G-A) and a gate-to-anode capacitance C(G-A) asmentioned previously. In addition, a voltage source indicated by V,,,,,,is connected in series with R in the gate circuit. It is proposed thattheanode current which flows when silicon controlled rectifier 68 is on,flows through resistive component R(A-K) and is responsible forsubstantially producing the voltage V135 at gate 76, where voltage V135is a function of the currentI flowing through resistance R(A-K). Whenthe current I, reaches a low value, V135 decreases so that current 137Ias described previously, may flow into gate 76 through R and through theresistive component of the gate-to-cathode circuit R(GK) whereuponvoltage V135 is sustained until I once again reaches a sufficiently highvalue to maintain the silicon controlled rectifier 68 in the on state.Equivalent relay contact 200 is closed to indicate that siliconcontrolled rectifier 68 is in the conducting mode.

FIG. 12 shows a second embodiment of the invention. The embodiment ofthe invention shown in FIG. 12 is generally the same as the firstembodiment of the invention shown in FIG. 2 with two exceptions. First,the hysteresis function is provided by different means and second, thisembodiment does not rely on the fact that the voltage of the gate 76increases when the silicon controlled rectifier 68 is turned on.Consequently, capacitor 274 shown in FIG. 12 does not perform the samefunction as capacitor 65, shown in FIG. 2. Rather, capacitor 274 ismerely useful in helping to trigger silicon controlled rectifier 68 intothe on state. Diode 272 is used to prevent high reverse voltages frombeing impressedbetween the cathode 74 and gate 76 of the siliconcoritrolled rectifier or thyristor 68. Resistor 270 is a ballastresistor used to absorb extra energy in the triggering network 64B ofthe silicon controlled rectifier 68 of static gating means 668.Primarily, the main difference between the first embodiment of theinvention and the second embodiment of the invention as shown in FIG.12, is the use of a different hysteresis generating means 648 whichdiffers significantly from the hysteresis generating means 64 shown inFIG. 2. For this reason, it is to be understood that the operation ofthe transducer 10 and the slave or complementary circuit 105 shown inFIG. 12 is the same as the operation of 50B is slightly different fromvoltage comparator means 50 as shown in FIG. 2, in that an additionalresistor 58B and a diode 230 is added to the series combination ofcomponents connected between terminals 47A and 49A in FIG. 12. Resistors58A and 58B are in combination, and generally but not necessarily, equalto the resistance value in ohms of resistor 58 previously described inconnection with FIG. 2. Resistor 60A is generally the same as resistor60 shown in FIG. 2 and diode 230 is added for temperature compensation.The particular operation of the voltage boosting network or hysteresisnetwork 648 is as follows. Assuming that voltage V52 at junction pointor terminal 47A is sufficiently low so that silicon controlled rectifier68 is not energized because sufficient voltage has not been impressedupon gate terminal 76 to energize the controlled rectifier 68, it willbe noted that substantially the entire voltage of the alternatingcurrent source of voltage 42 is impressed across terminals A and 70Dwhich, in turn, are connected to resistors 260 and 262. Resistors 260and 262 are connected in series circuit relationship, having a commonterminal 264 connected to the base 256 of a semiconductor transistor250. Since the voltage 42 across voltage divider combination 260 and 262is relatively large, transistor 250 is turned on or saturated, causingcurrent 6031 to flow through collector load resistor 268 into thecollector 254 of transistor 250 and out of the emitter 252 of transistor250 to return conductor or line 700. Concurrently, current 602I flowsthrough voltage divider combination 58A and 60A imposing voltage V134 atterminal 62 and, consequently, on gate 76 of silicon controlledrectifier 68. As was mentioned, the amount of current 602I flowingthrough resistors 58A and 60A is insufficient to create a voltage V134which can trigger silicon controlled rectifier 68 on. Current 601] whichis equal to the total of current 602] and current 603I, flows fromterminal 47A; As rotor 14 is moved in a counterclockwise direction19ACW, the voltage V52 and current 601I available at terminal 47Aincrease toward predetermined values and V134 increases correspondinglyto the value where V,,,,,,, as shown in FIG. 6, is exceeded and siliconcontrolled rectifier 68 is actuated to a conducting condition. When thisoccurs, the voltage drop between terminals 70A and 70D decreases tosubstantially zero voltage or to the voltage drop across a conductingSCR 68. When that happens, the voltage at terminal 264 or base oftransistor 250 decreases to a value which is insufficient to maintaintransistor 250 on or which causes it to cease to conduct. Therefore,current 603I ceases to flow and since current 601I remains constant orat a predetermined value, current 6021 must increase. The voltage dropthrough resistor 60A therefore increases and, as a consequence, thevoltage V134 at terminals 62 increases even though rotor 14 must nothave been turned further to a different position. This means that rotor14 must be rotated in the opposite direction or clockwise directionll9CW a significant amount to cause current 701i and consequently,current 602 I to decrease to such a value that V134 at junction point 62will decrease below the minimum firing voltage V of silicon controlledrectifier 68. If this happens, of course, silicon controlled rectifier68 will cease to conduct and substantially the full magnitude of voltagesource 42 will be impressed across the series circuit which includesresistors 26ll and 262mm turning transistor 2 0 on and providing a pathfor current 6031 to flow, whereupon the operating cycle of the overallcircuit has been completed.

It is to be understood that the transducer or switching device 10 mayhave a stator 12 which is not necessarily a laminated stator. Thelaminations such as 12A and 12B are added to prevent circulating eddycurrents and associated heating and any magnetic material which may beused to prevent or reduce eddy currents without being laminated issuitable for use in transducer section 12. It is also to be understoodthat pole windings 28, 30 and 32 may be wound in various configurationsupon the associated poles of stator 12. It is also to be understood thatthe direction of rotation of rotor M may be changed fromcounterclockwise to clockwise for any particular switching functiondepending upon the way in which the coils 28, 30 and 32 are wound onpoles 2t), 22 and 24 respectively, and the way that the coil leads areconnected to the bridge circuits 52 and 54, for example. It is also tobe understood that the circuitry to be controlled by switch 68 orswitching section 66 may be single-phase or multiphase and additionallyis not limited to either of these alternatives. The same applies for theslave or complementary circuit 105. In general it is to be understoodthat both the main switching circuit as indicated at 66 and the slave orcomplementary circuit 105 may be of the same basic type as disclosedwith certain variations. However, any alternative complementary circuitwhich may be coupled in some working manner to the electrical pulses ofthe main switching circuit 66 may be used. In addition, circuit 105which heretofore has been called a complementary or slaved oppositelyphased switching circuit, may act in tandem or in parallel with the mainswitching circuit 66; that is, switching circuit 105 and switchingcircuit 66 may both cause external circuits to open and closesimultaneously rather than to operate differently at a particular timeas disclosed. It is also to be understood that the switching elements 68and 100 are not necessarily limited to the silicon controlled rectifiertype of switching element as disclosed. They may include any type ofsolid state switching device which approximates the propertiespreviously discussed. It is also to be understood that limit switch 40may omit the extra switching section 105 or corresponding transformer 85in a particular application.

That is, switch 40 may merely comprise a single switching section 66. Itis also to be understood that the surface B of rotor M is preferablylarger than the surface 26C of pole 26 in order that the magnetic fluxflowing in the air gap between surface 26C and 158 during operation ofthe transducer or switching device M, will not be forced to flow througha magnetic circuit which varies substantially in reluctance as rotor 14is turned. It is also to be understood that the curves and equivalentcircuits shown in FIGS. 3 through 11 represent proposed theories toassist in understanding the operation of the switching circuit 40 andthat the prac tice of the applicants invention as disclosed does notdepend upon the substantiation of any or all of the theories proposedand equivalent circuits derived with respect to the curves andequivalent circuits discussed. It is also to be understood that thealternating current voltage source 42 need not necessarily be a sourceof sinusoidally shaped alternating current but may be any source ofalternating or pulsating current regardless of the shape. It is also tobe understood that resistors 268, 260 and 262 may not be necessary toinsure the operation of the hysteresis generator or circuit 643 as shownin FIG. 12, but rather that some or all of said resistors 268, 260 and262 may be omitted depending upon other circuit conditions in circuit40A. Also, it is to be understood that although this invention may beused in the control of a machine tool, it is not limited to suchapplications and may be used in any application where a limit of someoperation or movement is to be sensed and a corresponding output orresponse results when this limit is reached.

The apparatus embodying the teachings of this invention has severaladvantages. For example, the hysteresis means disclosed is such thatmechanical vibration in the transducer section 10, extraneous noisepickup by components of the switch or aging or slight variation in thevalues of the components of the switch, will not cause a once triggeredswitch to deenergize when, in fact, a predicted happening or event whichis to cause the denergization has not occurred. Another advantage is thefact that intrinsic capacitance and resistance of a silicon controlledrectifier may be utilized to actuate a more positive turning on of theswitching circuit by proper selection of the external adjacentcomponents connected to the silicon controlled rectifier gate. Stillanother advantage is the fact that the total area through which magneticflux must flow in the transducer or mechanical switch, may remainsubstantially unchanged during the operation of the transducer. Anotheradvantage is the fact that the transducer or switching device is moresensitive to slight angular changes in rotor position so that theangular positions of the rotor which determine turn on and turn off ofthe associated switching means can be predetermined with greateraccuracy. Finally, the transducer has the advantage of not acting asmerely a variable reluctance transducer, but actually produces an outputcurrent which may be controlled by the operation of the transducer.Another advantage is that because the magnetic circuit is essentially aclosed loop the magnetizing current is low and hence the input impedanceis high. Therefore, the limit switch can be energized from voltagesources of different values with virtually no need to use an electricalcurrent limiting resistor.

We claim as our invention:

1. Electrical apparatus comprising a gated static switching meansadapted to control electrical current flowing through a load, a voltageboosting means connected to the gate of said static switching means tobe electrically charged periodically when said gated static switchingmeans is on, said voltage boosting means being operative to periodicallyrelease said electrical charge to said gate of said gated staticswitching means to keep said gated static switching means on duringpredetermined operating conditions, a generally stationary magneticstructure and a generally movable adjacent magnetic member cooperatingtherewith, said stationary magnetic structure and said movable magneticmember comprising a path for magnetic flux, said stationary structurehaving disposed thereon first, second and third inductive coils, saidthird inductive coil being connected to a source of alternating currentand disposed to produce magnetic flux in said stationary structure andsaid movable member when energized from said source of alternatingcurrent, said magnetic flux having three component paths of flow, afirst component path comprising a first portion of said movable memberand that portion'only of said stationary structure upon which said-firstcoil is disposed, a second component path including a second portion ofsaid movable member and that portion only of said stationary structureupon which said second coil is disposed and a third component pathincluding a third portion of said movable member and excluding anyportion of said stationary structure upon which either said first orsecond coil is disposed, the amount of magnetic flux in said first andsaid second component oaths being generally variable in inverserelationship to each other regardless of the position of said movablemember with respect to said stationary member within a limited range,the total amount of said magnetic flux in said first and said secondcomponent paths being significantly less than the amount of saidmagnetic flux in said third component path at any time, said movablemember being disposed with respect to said first and said secondcomponent paths in such a manner that a small change in the position ofsaid movable member provides a relatively large change in the amount ofsaid flux in said first and said second component paths, the totalmagnetic flux in said first, said second and said third component pathsremaining generally unchanged regardless of the position of said movablemember with respect to said stationary member, a voltage comparatormeans electrically connected at its input to said first and said secondcoils and at its output to said gate, said first and second inductivecoils having induced therein in response to said magnetic flux flowingtherethrough first and second alternating electrical currentsrespectively, said first and second alternating currents being appliedto said voltage comparator means at said input to produce aunidirectional current voltage at said output to energize said gate,said movable member being actuable to control the magnitude and polarityof said unidirectional current voltage at said output, said voltageboosting means being connected to maintain said unidirectional currentvoltage at said gate after said gate is energized during limitedrelative motion between said stationary member and said movable member.

2. Electrical apparatus as claimed in claim 1 wherein said first, secondand third inductive coils are all wound on said stationary magneticstructure.

3. Electrical apparatus as claimed in claim 2 wherein said stationarymagnetic structure comprises first, second and third poles, said firstand said second poles being oppositely disposed, said third inductivecoil being wound on said third pole, said first and second inductivecoils being wound on said first and second poles, respectively, tocontrol said unidirectional current voltage which is produced by saidvoltage comparator means to be either negative or positive and to besubstantially proportional to the relative position of said movablemagnetic member with respect to said stationary magnetic member over alimited range of movement of said movable magnetic member.

4. Electrical apparatus as claimed in claim 3 wherein said stationarymagnetic member comprises-a fourth pole, said stationary magnetic memberbeing shaped to conduct magnetic flux in closed paths from said thirdpole through said movable magnetic member to said first, second andfourth poles, and back to said third pole through said stationarymagnetic structure.

5. Electrical apparatus as claimed in claim 4 wherein said movablemagnetic member comprises a rotor, said rotor being pivotally supportedadjacent to said stationary magnetic structure so that it may rotate,said rotation being such that a substantial portion of said magneticflux flows through said rotor, said main portion of said magnetic fluxbeing conducted through said rotor to said fourth pole of saidstationary magnetic member and back to said third pole in closed paths,lesser portions of said flux being conducted through said first andsecond poles of said stationary member and back to said third pole ofsaid stationary member in closed paths, said rotor being actuablc ineither clockwise or counterclockwise directions, the relative amounts ofsaid magnetic flux passing through said first and second poles beingdependent on the angular position of said rotor, said rotor having areference position with respect to said stationary structure wherebysaid flux flowing through said first and second poles is substantiallyequal when said rotor is disposed in said reference position to therebyapply substantially equal and opposite first and second alternatingcurrents to said voltage comparator with substantially no voltage beingapplied to said gate, said first and second inductive coils being woundin predetermined directions so that said first and second alternatingcurrents generally flow in opposite directions with respect to eachother.

6. Electrical apparatus as claimed in claim 5, said gated solid stateswitching means comprising a silicon controlled rectifier havingintrinsic cathode resistance, anode, cathode and gate terminals, saidanode and cathode being adapted to be connected to a source ofunidirectional current voltage. I

7. Electrical apparatus as claimed in claim 6 wherein saidunidirectional source of voltage comprises means for providing apulsating rectified alternating voltage, the period of time that saidsilicon controlled rectifier is maintained on after said rectifiedalternating voltage has decreased to a value less than said minimum gatecontrol voltage being longer than the time required for said rectifiedalternating voltage to increase to a value sufficient to maintain saidsilicon controlled rectifier in the on state, to thereby maintain saidsilicon controlled rectifier on continuously to conduct said rectifiedalternating current through said load substantially continuously.

8. Electrical apparatus as claimed in claim 6, wherein said voltageboosting means comprises a load circuit, a static device with first andsecond load terminals and a control terminal; a voltage feedback means,with first and second input terminals and an output terminal, said Zllvoltage comparator including a first and second current rectifying meansand voltage divider means comprising first and second input terminalsand first and second output terminals, said first rectifying means beingadapted to rectify said first alternating electrical current from saidfirst inductive coil to produce a first unidirectional rectifiedcurrent, said second rectifying means being adapted to rectify saidsecond alternating electrical current from said second inductive coil toproduce a second unidirectional rectified current, said first inputterminal of said voltage divider means being connected to said firstrectifying means, said'second input terminal of said voltage dividermeans being connected to said second rectifying means, one of saidrectifying means supplying unidirectional electrical current to saidvoltage divider means, the other of said rectifying means absorbingsubstantially the same electrical current from said voltage dividermeans, said load circuit being connected between said first outputterminals of said voltage dividing means and said first load terminal ofsaid static device, said second load terminal of said static devicebeing connected to both of said rectifying means, said second outputterminal of said voltage divider means being electrically connected tosaid gate of said silicon controlled rectifier, said anode of saidsilicon controlled rectifier being connected electrically to said firstinput terminal of said voltage feedback means, said second inputterminal of said voltage feedback means being connectedto both of saidcurrent rectifying means, said output terminal of said voltage feedbackmeans being connected electrically to said control terminal of saidstatic device, said rotor being actuable to a position with respect tosaid reference position which causes sufficient first and second saidrectified output currents to flow through said voltage divider means toproduce said minimum gate control voltage at said second outputterminals of said voltage divider means, and to actuate said siliconcontrolled rectifier to be turned on so as to cause said load current toflow through said load, said static device being turned off by thechange in voltage at the anode terminal of said silicon controlledrectifier, said change in voltage being transferred through said voltagefeedback means to said control terminal of said static device to turnthe said static device off and in crease the voltage at said secondoutput terminal of said voltage divider means, to thereby maintain saidgate voltage at a higher value than would otherwise result when saidsilicon controlled rectifier is conducting, a greater rotation of saidrotor being required in the opposite direction with respect to saidreference position to actuate said silicon controlled rectifier tosubstantially cease to conduct.

9. Electrical apparatus as claimed in claim 8 wherein said load circuitcomprises a resistor, said static device comprises a transistor, saidfirst load terminal comprises the collector of said transistor, saidsecond load terminal comprises the emitter of said transistor, saidcontrol terminal comprises the base of said transistor, said voltagefeedback means comprises first and second resistors connected in seriescircuit relationship and said output terminal forms a junction pointbetween said first and second resistors, said voltage divider meanscomprising third, fourth and fifth resistors, and a diode, with saidthird resistor being connected between said first input terminal andsaid first output terminal of said voltage divider means, said fourthresistor being connected between said first output terminal and saidsecond output terminal of said voltage divider, said fifth resistorbeing connected in series circuit relationship with said diode betweensaid second output terminal and said second input terminal of saidvoltage divider means, said diode being connected to pass current in theforward direction from said second output terminal to said second inputterminal of said voltage divider means, said first rectifying meansoperating as a source of electrical current and causing said firstvoltage divider means input terminal to be relatively positive inpotential and said second input terminal of said voltage divider meansto be relatively negative in potential, and said second rectifying meansoperating generally as a means for receiving said electrical current.

10. Electrical apparatus as claimed in claim 9 wherein said electricalapparatus additionally includes a machine tool disposed to change therotary position of said rotor as a result of the operation of saidmachine tool causing said silicon controlled rectifier to switch on oroff to control an operating function of said machine tool.

11. The combination as claimed in claim 9 wherein an auxiliarytransformer and auxiliary switching circuit are provided, said auxiliaryswitching circuits being electromagnetically linked through saidtransformer windings to said silicon controlled rectifier, saidauxiliary switching circuit being energized when substantial electricalcurrent flows in said load circuit and said auxiliary transformer.

12. The combination as claimed in claim 10, said auxiliary switchingcircuit being deenergized when substantial electrical current flows insaid load circuit.

13. Electrical apparatus comprising a silicon controlled rectifierhaving an anode, a cathode and a gate terminal and intrinsic cathoderesistance said silicon controlled rectifier being connected at itsanode and cathode in electrical circuit relationship with a load so thatelectrical load current may flow through said load and saidanode-to-cathode circuit of said silicon controlled rectifier when saidsilicon controlled rectifier is in the on state, said anode-to-cathodecircuit of said silicon controlled rectifier being empowered by a sourceof unidirectional voltage disposed in series circuit relationshiptherewith and with said load, a stationary magnetic structure, a rotorpivotally supported adjacent to said stationary magnetic structure, andbeing magnetically conductive, said stationary magnetic structure havingfirst, second, third and fourth poles, said first and said second polesbeing oppositely disposed, said first and said second poles having woundthereon first and second electrically conducting inductive coils,respectively, said third pole having wound thereon a third inductivecoil which is electrically connected to a source of alternating current,said alternating current when flowing through said third coil producingmagnetic flux in said stationary magnetic structure and said rotor, themain portion of said magnetic fiux flowing from said third pole throughsaid stationary magnetic structure through said fourth pole and saidrotor to return to said third pole, lesserportions of said magnetic fluxflowing from said third pole through said stacomparator with input andoutput terminals, said first and said second inductive coils beingelectrically connected in polarity opposing circuit relationship withthe input terminal of said voltage comparator, the output terminal ofsaid voltage comparator being connected in electrical circuitrelationship with said gate of said silicon controlled rectifier,alternating electrical current flowing in said first and said secondinductive coils in relationship to the angular displacement of saidrotor from said reference position, said alternating electrical currentsbeing compared by said voltage comparator to provide a unidirectionalcurrent voltage, the magnitude and polarity of which are proportional tothe relative angular displacement of said rotor from said referenceposition over a limited range, substantially no unidirectional currentvoltage being produced by said voltage comparator when said rotor isdisposed in said reference position, a predetermined value of saidunidirectional current voltage causing said silicon controlled rectifierto be turned on thus causing unidirectional current to flow in saidload, a voltage boosting means connected in electrical circuitrelationship with said gate, said voltage boosting means beingperiodically electrically charged when said silicon controlled rectifieris on, said voltage boosting means periodically releasing saidelectrical charge to said gate to maintain said silicon controlledrectifier in the on state when said rotor is moved in such a directionas to turn said silicon controlled rectifier off by changing the valueof the unidirectional current voltage on said gate, said rotor beingmoved an incremental distance in said same direction to thereby turnsaid silicon controlled rectifier off thus creating hysteresis in theswitching operation of said silicon controlled rectifier.

14. Electrical apparatus as claimed in claim 13, wherein said voltageboosting means includes a capacitive element connected in circuitrelation with said intrinsic cathode resistance of said siliconcontrolled rectifier and said voltage comparator of said variable sourceof voltage, said intrinsic cathode resistance being electricallyconnected to said capacitive element and said voltage comparator throughsaid gate terminal, said capacitive element being electrically chargedto provide an increase in voltage at said gate terminal when saidsilicon controlled rectifier is turned on by the action of said variablesource of voltage, said increase in said gate terminal voltage being dueto flow of said load current, said increase in said gate terminalvoltage causing charge to flow into said capacitive element to bestored, said capacitive element being connected to later discharge aportion of said stored charge to said gate terminal and through saidintrinsic cathode resistance to maintain said gate voltage at asufficient value to actuate said silicon controlled rectifier to remainon for a predetermined period of time after said unidirectional sourceof voltage has decreased to a value less than said minimum gate controlvoltage.

15. Electrical inductive apparatus comprising a generally stationarymagnetic structure and a generally movable adjacent magnetic membercooperating therewith, said stationary magnetic structure and saidmovable magnetic member comprising a path for magnetic flux, saidstationary structure having disposed thereon first, second and thirdinductive coils, said third inductive coil being connected in circuitrelationship to a source of alternating current and being disposed toproduce magnetic flux in said stationary magnetic structure and saidmovable magnetic member when energized from said source of alternatingcurrent, said magnetic flux having three component paths of flow, afirst component path including a first portion of said movable memberand that portion only of said stationary structure upon which said firstcoil is disposed, a second component path including a second portion ofsaid movable member and that portion only of said stationary structureupon which said second coil is disposed, and a third component pathincluding a third portion of said movable member and excluding anyportion of said stationary structure upon which either said first orsaid second coil is disposed, the amount of magnetic flux in said firstand said second component paths being generally variable in inverserelationship to each other regardless of the position of said movablemember with respect to said stationary member at any time, the totalamount of said magnetic flux in said first and said second componentpaths being significantly less than the amount of said magnetic flux insaid third component path at any time, said movable member beingdisposed with respect to said first and said second component paths insuch a manner that a small change in the relative position of saidmovable member provides a relatively large change in the amount of saidflux in said first and said second component paths, the total magneticflux in said first, said second and said third component paths remaininggenerally unchanged regardless of the position of said movable memberwith respect to said stationary member, a plurality of electrical loadssaid first and said second inductive coils being disposed to produce inresponse to said magnetic flux first and second alternating electricalcurrents in said first and second coils respectively when said first andsaid second coils are connected in circuit relationship to at least oneof said electrical loads.

16. The combination as claimed in claim 15 wherein said first, secondand third inductive coils are all wound on said stationary magneticstructure.

17. The combination as claimed in claim 16 wherein said stationarymagnetic structure includes first, second and third poles, and saidplurality of loads includes first and second electrical loads, saidfirst and second poles being oppositely disposed, said third inductivecoil being wound on said third pole, said first and second inductivecoils being wound on said first and second poles, respectively, so thatsaid first and said second currents in said first and second coils andsaid first and second loads are substantially proportional to therelative position of said movable magnetic member with respect to saidstationary magnetic member over a limited range of movement of saidmovable magnetic member.

18. The combination as claimed in claim 17 wherein said stationarymagnetic member includes a fourth pole, said stationary magnetic memberbeing shaped to conduct magnetic flux in closed paths from said thirdpole through said movable magnetic member to'said first, second andfourth poles, and back to said third pole through said stationarymagnetic structure.

19. The combination as claimed in claim 18 wherein said movable magneticmember comprises a rotor, said rotor being pivotally supported adjacentto said stationary magnetic structure so that it may rotate, saidrotation being such that a substantial portion of said magnetic fluxflows through said rotor, said main portion of said magnetic flux beingconducted through said rotor to said fourth pole of said stationarymagnetic member and back to said third pole in closed paths, lesserportions of said flux being conducted through said first and secondpoles of said stationary member and back to said third pole of saidstationary member in closed paths, said rotor being actuable in eitherclockwise or counterclockwise directions, the relative amounts of saidmagnetic flux passing through said first and second poles beinggenerally dependent upon the angular position of said rotor, said rotorhaving a reference position with respect to said stationary structurewhereby the said flux flowing through said first and second poles issubstantially equal when said rotor is disposed in said referenceposition to thereby apply substantially equal and opposite first andsecond alternating currents to said firstiand second electrical loads,said first and second inductive coils being wound in predetermineddirections so that said first and second alternating currents flow inopposite directions.

20. The combination as claimed in claim 19 wherein said first and secondelectrical loads comprise corresponding parts of an electrical voltagecomparator network, said voltage comparator having an indicatingterminal adaptable for external connection, the voltage potential atsaid indicating terminal being generally proportional to the angularposition of said rotor with respect to said reference.

Zll. The combination as claimed in claim 19 wherein said electricalapparatus comprises a switch.

22. Electrical inductive apparatus comprising an electrical voltagecomparator network, said voltage comparator network having inputterminals and an output terminal adapted for external connection, astationary magnetic structure, a rotor pivotally disposed adjacent tosaid magnetic structure, said rotor being magnetically conductive, saidstationary magnetic structure having first, second, third and fourthpoles disposed thereon, said first and second poles being oppositelydisposed, said first and second poles having wound thereon first andsecond electrically conducting inductive coils, said third pole havingwound thereon a third inductive coil which is electrically connected incircuit relationship to a source of alternating current, saidalternating current flowing through said third coil producing magneticflux in said stationary magnetic structure and said rotor, the remainingportion of said magnetic flux flowing from said third pole through saidstationary magnetic structure, through said fourth pole and said rotorto return to said third pole, lesser portions of said magnetic fluxflowing from said third pole through said stationary magnetic structurethrough said first and said second poles in parallel paths through saidrotor and back to said third pole, said rotor having a referenceposition relative to said stationary magnetic structure at whichposition generally equal amounts of said magnetic flux flow in saidfirst and said second poles because of the disposition of said rotor,said rotor being pivotally rotatable about said pivot from saidreference position in either'a' clockwise or counterclockwise directionto change the amount of flux flowing through said first and said secondpoles, said first and said second inductive coils being electricallyconnected in polarity opposing electrical circuit relationship to theinput terminals of said voltage comparator network, alternating currentflowing in said first and said second inductive coils in relationship tothe angular displacement of said rotor with respect to said referenceposition, said output terminal of said voltage comparator network havinga voltage potential thereat which is generally related to the angularposition of said rotor with respect to said reference position.

23. The combination as claimed in claim 22 wherein said electricalapparatus comprises a switch.

1. Electrical apparatus comprising a gated static switching meansadapted to control electrical current flowing through a load, a voltageboosting means connected to the gate of said static switching means tobe electrically charged periodically when said gated static switchingmeans is on, said voltage boosting means being operative to periodicallyrelease said electrical charge to said gate of said gated staticswitching means to keep said gated static switching means on duringpredetermined operating conditions, a generally stationary magneticstructure and a generally movable adjacent magnetic member cooperatingtherewith, said stationary magnetic structure and said movable magneticmember comprising a path for magnetic flux, said stationary structurehaving disposed thereon first, second and third inductive coils, saidthird inductive coil being connected to a source of alternating currentand disposed to produce magnetic flux in said stationary structure andsaid movable member when energized from said source of alternatingcurrent, said magnetic flux having three component paths of flow, afirst component path comprising a first portion of said movable memberand that portion only of said stationary structure upon which said firstcoil is disposed, a second component path including a second portion ofsaid movable member and that portion only of said stationary structureupon which said second coil is disposed and a third component pathincluding a third portion of said movable member and excluding anyportion of said stationary structure upon which either said first orsecond coil is disposed, the amount of magnetic flux in said first andsaid second component oaths being generally variable in inverserelationship to each other regardless of the position of said movablemember with respect to said stationary member within a limited range,the total amount of said magnetic flux in said first and said secondcomponent paths being significantly less than the amount of saidmagnetic flux in said third component path at any time, said movablemember being disposed with respect to said first and said secondcomponent paths in such a manner that a small change in the position ofsaid movable member provides a relatively large change in the amount ofsaid flux in said first and said second component paths, the totalmagnetic flux in said first, said second and said third component pathsremaining generally unchanged regardless of the position of said movablemember with respect to said stationary member, a voltage comparatormeans electrically connected at its input to said first and said secondcoils and at its output to said gate, said first and second inductivecoils having induced therein in response to said magnetic flux flowingtherethrough first and second alternating electrical currents flowingtherein, respectively, said first and second alternating currents beingapplied to said voltage comparator means at said input to produce aunidirectional current voltage of said output to energize said gate,said movable member being actuable to control the magnitude and polarityof said unidirectional current voltage at said output, said voltageboosting means being connected to maintain said unidirectional currentvoltage at said gate after said gate is energized during limitedrelative motion between said stationary member and said movablemember.
 1. Electrical apparatus comprising a gated static switchingmeans adapted to control electrical current flowing through a load, avoltage boosting means connected to the gate of said static switchingmeans to be electrically charged periodically when said gated staticswitching means is on, said voltage boosting means being operative toperiodically release said electrical charge to said gate of said gatedstatic switching means to keep said gated static switching means onduring predetermined operating conditions, a generally stationarymagnetic structure and a generally movable adjacent magnetic membercooperating therewith, said stationary magnetic structure and saidmovable magnetic member comprising a path for magnetic flux, saidstationary structure having disposed thereon first, second and thirdinductive coils, said third inductive coil being connected to a sourceof alternating current and disposed to produce magnetic flux in saidstationary structure and said movable member when energized from saidsource of alternating current, said magnetic flux having three componentpaths of flow, a first component path comprising a first portion of saidmovable member and that portion only of said stationary structure uponwhich said first coil is disposed, a second component path including asecond portion of said movable member and that portion only of saidstationary structure upon which said second coil is disposed and a thirdcomponent path including a third portion of said movable member andexcluding any portion of said stationary structure upon which eithersaid first or second coil is disposed, the amount of magnetic flux insaid first and said second component oaths being generally variable ininverse relationship to each other regardless of the position of saidmovable member with respect to said stationary member within a limitedrange, the total amount of said magnetic flux in said first and saidsecond component paths being significantly less than the amount of saidmagnetic flux in said third component path at any time, said movablemember being disposed with respect to said first and said secondcomponent paths in such a manner that a small change in the position ofsaid movable member provides a relatively large change in the amount ofsaid flux in said first and said second component paths, the totalmagnetic flux in said first, said second and said third component pathsremaining generally unchanged regardless of the position of said movablemember with respect to said stationary member, a voltage comparatormeans electrically connected at its input to said first and said secondcoils and at its output to said gate, said first and second inductivecoils having induced therein in response to said magnetic flux flowingtherethrough first and second alternating electrical currents flowingtherein, respectively, said first and second alternating currents beingapplied to said voltage comparator means at said input to produce aunidirectional current voltage of said output to energize said gate,said movable member being actuable to control the magnitude and polarityof said unidirectional current voltage at said output, said voltageboosting means being connected to maintain said unidirectional currentvoltage at said gate after said gate is energized during limitedrelative motion between said stationary member and said movable member.2. Electrical apparatus as claimed in claim 1 wherein said first, secondand third inductive coils are all wound on said stationary magneticstructure.
 3. Electrical apparatus as claimed in claim 2 wherein saidstationary magnetic structure comprises first, second and third poles,said first and said second poles being oppositely disposed, said thirdinductive coil being wound on said third pole, said first and secondinductive coils being wound on said first and second poles,respectively, to control said unidirectional current voltage which isproduced by said voltage comparator means to be either negative orpositive and to be substantially proportional to the relative positionof said movable magnetic member with respect to said stationary magneticmember over a limited range of movement of said movable magnetic member.4. Electrical apparatus as claimed in claim 3 wherein said stationarymagnetic member comprises a fourth pole, said stationary magnetic memberbeing shaped to conduct magnetic flux in closed paths from said thirdpole through said movable magnetic member to said first, second andfourth poles, and back to said third pole through said stationarymagnetic structure.
 5. Electrical apparatus as claimed in claim 4wherein said movable magnetic member comprises a rotor, said rotor beingpivotally supported adjacent to said stationary magnetic structure sothat it may rotate, said rotation being such that a substantial portionof said magnetic flux flows through said rotor, said main portion ofsaid magnetic flux being conducted through said rotor to said fourthpole of said stationary magnetic member and back to said third pole inclosed paths, lesser portions of said flux being conducted through saidfirst and second poles of said stationary member and back to said thirdpole of said stationary member in closed paths, said rotor beingactuable in either clockwise or counterclockwise directions, therelative amounts of said magnetic flux passing through said first andsecond poles being dependent on the angular position of said rotor, saidrotor having a reference position with respect to said stationarystructure whereby said flux flowing through said first and second polesis substantially equal when said rotor is disposed in said referenceposition to thereby apply substantially equal and opposite first andsecond alternating currents to said voltage comparator withsubstantially no voltage being applied to said gate, said first andsecond inductive coils being wound in predetermined directions so thatsaid first and second alternating currents generally flow in oppositedirections with respect to each other.
 6. Electrical apparatus asclaimed in claim 5, said gated solid state switching means comprising asilicon controlled rectifier having intrinsic cathode resistance, anode,cathode and gate terminals, said anode and cathode being adapted to beconnected to a source of unidirectional current voltage.
 7. Electricalapparatus as claimed in claim 6 wherein said unidirectional source ofvoltage comprises means for providing a pulsating rectified alternatingvoltage, the period of time that said silicon controlled rectifier ismaintained on after said rectified alternating voltage has decreased toa value less than said minimum gate control voltage being longer thanthe time required for said rectified alternating voltage to increase toa value sufficient to maintain said silicon controlled rectifier in theon state, to thereby maintain said silicon controlled rectifier oncontinuously to conduct said rectified alternating current through saidload substantially continuously.
 8. Electrical apparatus as claimed inclaim 6, wherein said voltage boosting means comprises a load circuit, astatic device with first and second load terminals and a controlterminal; a voltage feedback means, with first and second inputterminals and an output terminal, said voltage comparator including afirst and second current rectifying means and voltage divider meanscomprising first and second input terminals and first and second outputterminals, said first rectifying means being adapted to rectify saidfirst alternating electrical current from said first inductive coil toproduce a first unidirectional rectified current, said second rectifyingmeans being adapted to rectify said second alternating electricalcurrent from said second inductive coil to produce a secondunidirectional rectified current, said first input terminal of saidvoltage divider means being connected to said first rectifying means,said second input terminal of said voltage divider means being connectedto said second rectifying means, one of said rectifying means supplyingunidirectional electrical current to said voltage divider means, theother of said rectifying means absorbing substantially the sameelectrical current from said voltage divider means, said load circuitbeing connected between said first output terminals of said voltagedividing means and said first load terminal of said static device, saidsecond load terminal of said static device being connected to both ofsaid rectifying means, said second output terminal of said voltagedivider means being electrically connected to said gate of said siliconcontrolled rectifier, said anode of said silicon controlled rectifierbeing connected electrically to said first input terminal of saidvoltage feedback means, said second input terminal of said voltagefeedback means being connected to both of said current rectifying means,said output terminal of said voltage feedback means being connectedelectrically to said control terminal of said static device, said rotorbeing actuable to a position with respect to said reference positionwhich causes sufficient first and second said rectified output currentsto flow through said voltage divider means to produce said minimum gatecontrol voltage at said second output terminals of said voltage dividermeans, and to actuate said silicon controlled rectifier to be turned onso as to cause said load current to flow through said load, said staticdevice being turned off by the change in voltage at the anode terminalof said silicon controlled rectifier, said change in voltage beingtransferred through said voltage feedback means to said control terminalof said static device to turn the said static device off and increasethe voltage at said second output terminal of said voltage dividermeans, to thereby maintain said gate voltage at a higher value thanwould otherwise result when said silicon controlled rectifier isconducting, a greater rotation of said rotor being required in theopposite direction with respect to said reference position to actuatesaid silicon controlled rectifier to substantially cease to conduct. 9.Electrical apparatus as claimed in claim 8 wherein said load circuitcomprises a resistor, said static device comprises a transistor, saidfirst load terminal comprises the collector of said transistor, saidsecond load terminal comprises the emitter of said transistor, saidcontrol terminal comprises the base of said transistor, said voltagefeedback means comprises first and second resistors connected in seriescircuit relationship and said output terminal forms a junction pointbetween said first and second resistors, said voltage divider meanscomprising third, fourth and fifth resistors, and a diode, with saidthird resistor being connected between said first input terminal andsaid first output terminal of said voltage divider means, said fourthresistor being connected between said first output terminal and saidsecond output terminal of said voltage divider, said fifth resistorbeing connected in series circuit relationship with said diode betweensaid second output terminal and said second input terminal of saidvoltage divider means, said diode being connected to pass current in theforward direction from said second output terminal to said second inputterminal of said voltage divider means, said first rectifying meansoperating as a source of electrical current and causing said firstvoltage divider means input terminal to be relatively positive inpotential and said second input terminal of said voltage divider meansto be relatively negative in potential, and said second rectifying meansoperating generally as a means for receiving said electrical current.10. Electrical apparatus as claimed in claim 9 wherein said electricalapparatus additionally includes a machine tool disposed to change therotary position of said rotor as a result of the operation of saidmachine tool causing said siliCon controlled rectifier to switch on oroff to control an operating function of said machine tool.
 11. Thecombination as claimed in claim 9 wherein an auxiliary transformer andauxiliary switching circuit are provided, said auxiliary switchingcircuits being electromagnetically linked through said transformerwindings to said silicon controlled rectifier, said auxiliary switchingcircuit being energized when substantial electrical current flows insaid load circuit and said auxiliary transformer.
 12. The combination asclaimed in claim 10, said auxiliary switching circuit being deenergizedwhen substantial electrical current flows in said load circuit. 13.Electrical apparatus comprising a silicon controlled rectifier having ananode, a cathode and a gate terminal and intrinsic cathode resistancesaid silicon controlled rectifier being connected at its anode andcathode in electrical circuit relationship with a load so thatelectrical load current may flow through said load and saidanode-to-cathode circuit of said silicon controlled rectifier when saidsilicon controlled rectifier is in the on state, said anode-to-cathodecircuit of said silicon controlled rectifier being empowered by a sourceof unidirectional voltage disposed in series circuit relationshiptherewith and with said load, a stationary magnetic structure, a rotorpivotally supported adjacent to said stationary magnetic structure, andbeing magnetically conductive, said stationary magnetic structure havingfirst, second, third and fourth poles, said first and said second polesbeing oppositely disposed, said first and said second poles having woundthereon in first and second electrically conducting inductive coils,respectively, said third pole having wound thereon a third inductivecoil which is electrically connected to a source of alternating current,said alternating current when flowing through said third coil producingmagnetic flux in said stationary magnetic structure and said rotor, themain portion of said magnetic flux flowing from said third pole throughsaid stationary magnetic structure through said fourth pole and saidrotor to return to said third pole, lesser portions of said magneticflux flowing from said third pole through said stationary magneticstructure through said first and second poles, in parallel paths,through said rotor and back to said third pole, said rotor having areference position relative to said stationary magnetic structure atwhich position generally equal amounts of magnetic flux flow throughsaid first and said second poles, said rotor being rotatable about saidpivot from said reference position in either a clockwise or acounterclockwise direction to change the amount of flux flowing throughsaid first and said second poles, a voltage comparator with input andoutput terminals, said first and said second inductive coils beingelectrically connected in polarity opposing circuit relationship withthe input terminal of said voltage comparator, the output terminal ofsaid voltage comparator being connected in electrical circuitrelationship with said gate of said silicon controlled rectifier,alternating electrical current flowing in said first and said secondinductive coils in relationship to the angular displacement of saidrotor from said reference position, said alternating electrical currentsbeing compared by said voltage comparator to provide a unidirectionalcurrent voltage, the magnitude and polarity of which are proportional tothe relative angular displacement of said rotor from said referenceposition over a limited range, substantially no unidirectional currentvoltage being produced by said voltage comparator when said rotor isdisposed in said reference position, a predetermined value of saidunidirectional current voltage causing said silicon controlled rectifierto be turned on thus causing unidirectional current to flow in saidload, a voltage boosting means connected in electrical circuitrelationship with said gate, said voltage boosting means beingpEriodically electrically charged when said silicon controlled rectifieris on, said voltage boosting means periodically releasing saidelectrical charge to said gate to maintain said silicon controlledrectifier in the on state when said rotor is moved in such a directionas to turn said silicon controlled rectifier off by changing the valueof the unidirectional current voltage on said gate, said rotor beingmoved an incremental distance in said same direction to thereby turnsaid silicon controlled rectifier off thus creating hysteresis in theswitching operation of said silicon controlled rectifier.
 14. Electricalapparatus as claimed in claim 13, wherein said voltage boosting meansincludes a capacitive element connected in circuit relation with saidintrinsic cathode resistance of said silicon controlled rectifier andsaid voltage comparator of said variable source of voltage, saidintrinsic cathode resistance being electrically connected to saidcapacitive element and said voltage comparator through said gateterminal, said capacitive element being electrically charged to providean increase in voltage at said gate terminal when said siliconcontrolled rectifier is turned on by the action of said variable sourceof voltage, said increase in said gate terminal voltage being due toflow of said load current, said increase in said gate terminal voltagecausing charge to flow into said capacitive element to be stored, saidcapacitive element being connected to later discharge a portion of saidstored charge to said gate terminal and through said intrinsic cathoderesistance to maintain said gate voltage at a sufficient value toactuate said silicon controlled rectifier to remain on for apredetermined period of time after said unidirectional source of voltagehas decreased to a value less than said minimum gate control voltage.15. Electrical inductive apparatus comprising a generally stationarymagnetic structure and a generally movable adjacent magnetic membercooperating therewith, said stationary magnetic structure and saidmovable magnetic member comprising a path for magnetic flux, saidstationary structure having disposed thereon first, second and thirdinductive coils, said third inductive coil being connected in circuitrelationship to a source of alternating current and being disposed toproduce magnetic flux in said stationary magnetic structure and saidmovable magnetic member when energized from said source of alternatingcurrent, said magnetic flux having three component paths of flow, afirst component path including a first portion of said movable memberand that portion only of said stationary structure upon which said firstcoil is disposed, a second component path including a second portion ofsaid movable member and that portion only of said stationary structureupon which said second coil is disposed, and a third component pathincluding a third portion of said movable member and excluding anyportion of said stationary structure upon which either said first orsaid second coil is disposed, the amount of magnetic flux in said firstand said second component paths being generally variable in inverserelationship to each other regardless of the position of said movablemember with respect to said stationary member at any time, the totalamount of said magnetic flux in said first and said second componentpaths being significantly less than the amount of said magnetic flux insaid third component path at any time, said movable member beingdisposed with respect to said first and said second component paths insuch a manner that a small change in the relative position of saidmovable member provides a relatively large change in the amount of saidflux in said first and said second component paths, the total magneticflux in said first, said second and said third component paths remaininggenerally unchanged regardless of the position of said movable memberwith respect to said stationary member, a plurality of electrical loadssaid first and said second inductive coils bEing disposed to produce inresponse to said magnetic flux first and second alternating electricalcurrents in said first and second coils respectively when said first andsaid second coils are connected in circuit relationship to at least oneof said electrical loads.
 16. The combination as claimed in claim 15wherein said first, second and third inductive coils are all wound onsaid stationary magnetic structure.
 17. The combination as claimed inclaim 16 wherein said stationary magnetic structure includes first,second and third poles, and said plurality of loads includes first andsecond electrical loads, said first and second poles being oppositelydisposed, said third inductive coil being wound on said third pole, saidfirst and second inductive coils being wound on said first and secondpoles, respectively, so that said first and said second currents in saidfirst and second coils and said first and second loads are substantiallyproportional to the relative position of said movable magnetic memberwith respect to said stationary magnetic member over a limited range ofmovement of said movable magnetic member.
 18. The combination as claimedin claim 17 wherein said stationary magnetic member includes a fourthpole, said stationary magnetic member being shaped to conduct magneticflux in closed paths from said third pole through said movable magneticmember to said first, second and fourth poles, and back to said thirdpole through said stationary magnetic structure.
 19. The combination asclaimed in claim 18 wherein said movable magnetic member comprises arotor, said rotor being pivotally supported adjacent to said stationarymagnetic structure so that it may rotate, said rotation being such thata substantial portion of said magnetic flux flows through said rotor,said main portion of said magnetic flux being conducted through saidrotor to said fourth pole of said stationary magnetic member and back tosaid third pole in closed paths, lesser portions of said flux beingconducted through said first and second poles of said stationary memberand back to said third pole of said stationary member in closed paths,said rotor being actuable in either clockwise or counterclockwisedirections, the relative amounts of said magnetic flux passing throughsaid first and second poles being generally dependent upon the angularposition of said rotor, said rotor having a reference position withrespect to said stationary structure whereby the said flux flowingthrough said first and second poles is substantially equal when saidrotor is disposed in said reference position to thereby applysubstantially equal and opposite first and second alternating currentsto said first and second electrical loads, said first and secondinductive coils being wound in predetermined directions so that saidfirst and second alternating currents flow in opposite directions. 20.The combination as claimed in claim 19 wherein said first and secondelectrical loads comprise corresponding parts of an electrical voltagecomparator network, said voltage comparator having an indicatingterminal adaptable for external connection, the voltage potential atsaid indicating terminal being generally proportional to the angularposition of said rotor with respect to said reference.
 21. Thecombination as claimed in claim 19 wherein said electrical apparatuscomprises a switch.
 22. Electrical inductive apparatus comprising anelectrical voltage comparator network, said voltage comparator networkhaving input terminals and an output terminal adapted for externalconnection, a stationary magnetic structure, a rotor pivotally disposedadjacent to said magnetic structure, said rotor being magneticallyconductive, said stationary magnetic structure having first, second,third and fourth poles disposed thereon, said first and second polesbeing oppositely disposed, said first and second poles having woundthereon first and second electrically conducting inductive coils, saidthird pole having wound thereoN a third inductive coil which iselectrically connected in circuit relationship to a source ofalternating current, said alternating current flowing through said thirdcoil producing magnetic flux in said stationary magnetic structure andsaid rotor, the remaining portion of said magnetic flux flowing fromsaid third pole through said stationary magnetic structure, through saidfourth pole and said rotor to return to said third pole, lesser portionsof said magnetic flux flowing from said third pole through saidstationary magnetic structure through said first and said second polesin parallel paths through said rotor and back to said third pole, saidrotor having a reference position relative to said stationary magneticstructure at which position generally equal amounts of said magneticflux flow in said first and said second poles because of the dispositionof said rotor, said rotor being pivotally rotatable about said pivotfrom said reference position in either a clockwise or counterclockwisedirection to change the amount of flux flowing through said first andsaid second poles, said first and said second inductive coils beingelectrically connected in polarity opposing electrical circuitrelationship to the input terminals of said voltage comparator network,alternating current flowing in said first and said second inductivecoils in relationship to the angular displacement of said rotor withrespect to said reference position, said output terminal of said voltagecomparator network having a voltage potential thereat which is generallyrelated to the angular position of said rotor with respect to saidreference position.